“In Delhi, winter is the season for weddings. Ten months from that time, we can see a clear spike in the number of births in hospitals,” says Evelyn Kannan, general secretary of Trained Nurses’ Association of India, a national organization of nursing professionals. A seasonal spike in births isn’t restricted to Delhi alone, and is seen in other states and union territories also.

The data visualization below traces 21.2 million births in 2015-16—approximately 85% of all births in India—captured by the government’s Health Management Information System on a monthly basis. At an all-India level, more births happen in the second half of the calendar year than the first (53.7% versus 46.3%). The four months from August to November account for about 37% of all births. And more births are registered in September than in any other month (9.35%).

Among states, there are some that show significant monthly variance: for example, in Bihar, the average monthly share of births is 5.9% between April and June, but 10.2% between August and November. Then, there are certain states where the variance, though present, is less: like Karnataka and Maharashtra.